Actuator systems are known in the prior art and utilized for linearly moving and positioning a workpiece relative to a housing. Typical prior art electric actuators utilize a rotatable, externally threaded shaft, typically referred to as a screw, and a nut having internal threads matching the external threads of the screw. The nut is rotationally fixed and advances or retracts linearly along the screw in response to the rotation of the screw. The screw typically extends substantially from one end of the actuator to the other and is supported at each end. In this configuration, the middle portion of the screw will tend to sag, thereby creating an out-of-balance or eccentric condition when the screw is rotated. This out-of-balance condition is accentuated with a decrease in the diameter of the screw, an increase in the rotational speed of the screw or an increase in the length of the screw. Thus, for a given screw diameter, an unacceptable increase in the rotational speed or screw length, will cause the shaft to wobble or whip in jump rope fashion along the axis of the actuator. This not only places an upper limit on the acceptable linear speed and screw shaft length, but also leads to premature failure and wear of the screw shaft and nut and faulting of the rotary drive mechanism. Such vibrations and whipping action can also impair the accuracy of the positioning system.
Another problem encountered by these prior art actuators is that the loads encountered by the actuator rod are transferred ultimately through the rotary drive mechanism. The loads on the actuator rod are transferred through the nut to the screw shaft and then to the motor which rotationally drives the shaft. These loads adversely affect the motor life of the actuator.
Accordingly, there is a need in the art for a more robust actuator that is not limited by the use of a rotationally driven screw shaft.